Chef AB

chef-ab is a small library to activate code in cookbooks progressively in a cluster.

It works like an AB test with increasing population.

Usage

Very simple example in attribute file of :

# value before upgrade
default[:a_cookbook][:activate_experimental_feature] = false

upgrade = ChefAB::TimeLinearUpgrader.new(
  node_id: node['fqdn'], # we use fqdn as id for the migration
  start_time: Time.new(2014, 02, 11, 8, 30, 00, "+01:00"),
  end_time:   Time.new(2014, 02, 18, 8, 30, 00, "+01:00")
)

upgrade.execute do
  default[:a_cookbook][:activate_experimental_feature] = true
end

# sugar for easy status collect
default[:chef_ab][:experimental_feature_activation] = Time.at(upgrade.expected_activation)
default[:chef_ab][:experimental_feature_activated] = node[:a_cookbook][:activate_experimental_feature]

Another example, upgrading nodes exponentially depending on distance to a given ip address:

# value before upgrade
default[:a_cookbook][:activate_experimental_feature] = false

upgrade = ChefAB::TimeIPBasedUpgrader.new(
  node_id: node['ipaddress'],
  start_time: Time.new(2014, 02, 11, 8, 30, 00, "+01:00"),
  period: 3600, #going larger every hour
  first_node: "10.11.12.13"
)

upgrade.execute do
  default[:a_cookbook][:activate_experimental_feature] = true
end

Warning

• This lib is not a substitute to release management, it will solve only the issue of progressive update.
• It is meant to replace the ssh loop that many uses to upgrades server farms.
• This library does not give strong garantees on the number of servers that will activate code at the same time (see chef_throttle for that).